The authors report on the virological findings of 59 transplant recipients. The following procedures were used for the detection of human cytomegalovirus (HCMV) infection: detection of antiviral antibodies by ELISA, the detection of virus-coded antigens in the patients' leucocytes (HCMV antigenemia test), "accelerated" virus isolation using immunofluorescence (IF). Serial examinations revealed the HCMV infection in 12 patients following organ transplantation. The antigenemia test proved to be positive in all cases. Two third of the cases suffered from viremia. The virus specific serology possess diagnostic value only in every second acute illness. Since the antigenemia test used to be successful in the earliest phase of acute illnesses, the chance of effective chemotherapy can be increased significantly. The virus serological examinations are of essential importance during the pretransplantation screening of donors and recipients. The "accelerated" procedure of virus isolation experiments indicates the presence of infective HCMV within 1 to 4 days. Transplant recipients obtain new life perspectives, nevertheless, the modern diagnostic procedures may only support the prevention of life-threatening virus infections under the conditions of immunosuppression. The excellent mutual cooperation of the clinicians and diagnostic virologists seems to be at least as important condition of successful transplantation medicine as the high technology in surgery and clinical diagnostics.